The objective of the proposed research is to continue our studies of mesencephalic, pontine and medullary brainstem structures that are part of or modulate pathways to ocular motoneurons. Three different projects will be undertaken, each of which will employ alert behaving monkeys. Eye position will be accurately measured by an electromagnetic technique and the animal will be trained to track a small moving light spot while subjected to whole body oscillations and full-field movements of the visual world. In the first project, the behavior of the saccadic system will be studied by recording the activity of single cells that are thought to drive the brainstem circuitry involved in saccade generation. In the second project, various neurons believed to particiate in the vestibulo-ocular reflect that stbilizes the visual word on the retina during head rotations will be studied; experiments have been designed to test whether such neurons respond to visual and vestibular inputs and whether they project to ocular motoneurons. In the third project, the discharge patterns of neurons in the pretectum and the nuclei of the accessory optic tract will be recorded to determine their possible role in smooth pursuit eye movements and the optokinetic eye movements generated by full-field movement of the visual surroundings. Studies such as ours that demonstrate the pathways and neural structures involved in different types of eye movements have made it possible to devise clinical tests to diagnose the site of lesions or strokes that cause specific eye movement disorders in human patients.